1. Field of the Invention
This invention relates to a method of environmentally sealing fiber optic cable assemblies, and in particular to a method of sealing fiber optic cable assemblies from moisture by coating the prepared fiber terminations with a conformal coating before assembly to a coupler, connector, or backplane. The invention also relates to fiber optic cable assemblies in which the terminations have been environmentally sealed to protect the fiber from environmental degradation, and in particular to fiber optic cable assemblies having conformally coated fiber terminations.
2. Description of Related Art
It is well known that moisture can degrade the optical performance of fiber optic cable assemblies. In order to protect the fibers in a cable from moisture absorption, acrylate such as Corning's CPC6.RTM. and polyimide coatings are applied directly to the glass fibers to create a barrier to moisture.
While acrylate or polyimide coatings protect individual fibers during shipment and before preparation for termination, in order to terminate the fibers to a connector or alignment ferrule, the coating must be removed, leaving the fibers vulnerable to degradation due to moisture and other contaminants. The problem of fiber degradation due to exposure of the bare fibers following preparation for termination is especially significant in two situations: (1) following termination to an alignment ferrule but before installation, in an assembly plant or in the field, of the alignment ferrule in a fiber optic connector or coupler, and (2) in backplane terminations and other coupler assemblies where mechanical sealing is difficult and potting undesirable.
The first situation often arises because, during assembly of a fiber optic connector or housing, the fibers are often pre-terminated to alignment ferrules in one section of an assembly plant, and not installed in a sealed connector until later. Following termination to the ferrule, the terminated fibers must be stored until needed by the worker or section of the plant that assembles the fibers to the connectors or couplers. Storing and assembling the fiber optic connectors in clean rooms would be prohibitively expensive, and so the fibers are vulnerable during the period between termination to the ferrule and assembly to the connector or coupler, even where the connector or coupler in which the terminated fiber and ferrule is to be installed is adequately sealed.
It is also common for fibers to be pre-terminated to a ferrule and carried by workers for installation in the field, prior to which the portions of the fibers that have been exposed in preparation for termination are unprotected. Fiber optic terminations often require very high tolerances, and significant damage can occur during the interval between preparation of the cable for termination and the actual termination.
The second situation arises in applications, such as those involving optical backplanes of the type disclosed in U.S. patent application Ser. No. 09/006,193, field Jan. 12, 1998, now U.S. Pat. No. 5,980,312, herein incorporated by reference, where it is impractical to use mechanical sealing arrangements. While potting would solve the problem of degradation due to moisture, potting limits the flexibility of the fiber optic cables and makes it difficult to repair and replace individual cable assemblies, which is essential in backplane installations.
In view of the above, a need exists for a environmental sealing method and arrangement which can be used to seal a fiber optic termination immediately following termination of the fiber to an alignment ferrule or connector, thereby protecting the fiber even before it is installed in a sealed connector or coupling arrangement, and avoiding the need for potting in applications where the terminations would otherwise be completely unprotected.